1. Field of the Invention
The invention relates to techniques of tracking the position of a pupil of an eyeball, by directing light toward the eyeball and using a portion of the light reflected from the eyeball.
2. Description of the Related Art
Techniques have been in existence which are capable of tracking or monitoring the position of a pupil of an eyeball, by directing light toward the eyeball and using a portion of the light reflected from the eyeball.
Japanese Patent No. 3435160 discloses two exemplary conventional approaches of such techniques. These exemplary conventional approaches are in common in that a technique of tracking a pupil position is implemented together with an image display technique in which a desired image is projected directly onto a viewer's retina, by causing imaging light for displaying the image, to enter the retina through a viewer's pupil.
More specifically, in the first one of those two exemplary conventional approaches, display-purpose raster light is thrown toward an eyeball, and a portion of the raster light reflected from the surface of the eyeball is directed by a lens toward a position-sensing diode for light collection. The position-sensing diode is electrically coupled to an eye tracker for tracking or detecting a pupil position. Thus, in this exemplary conventional approach, the pupil position is tracked using imaging light originally produced for displaying a desired image.
In the second one of those two exemplary conventional approaches, there is an eye tracker including an infrared-light source. The infrared-light source illuminates an eyeball surface directly or indirectly with lower-luminance infrared light exclusively for the purpose of tracking of the pupil position.
In this approach, the eyeball surface is identified as a two-dimensional image through an optical combiner, a lens, and a Charge Coupled Device (CCD) sensor. The CCD sensor is formed as a two-dimensional array of a number of light-reception elements which create a two-dimensional array of a number of pixels.
Further, in this approach, an output signal of the CCD sensor is processed by a pupil position processor. More specifically, the pupil position processor performs image processing for the output signal of the CCD sensor, to thereby track a pupil position. The image processing is performed in a manner that a center position of the pupil is determined based on the center or the outline of an image of the eyeball captured by the CCD sensor.
Still further, in this approach, the infrared light is directed to the eyeball along an optical path separate from that along which imaging light enters the pupil, wherein the imaging light is originally produced for displaying a desired image.